A Mathematical Approach to Psych
by RascalFlattsS
Summary: With a serial killer on the loose, it will take the work of two unlikely police consultants to save day. That is if Charlie and Shawn can put aside their differences and work together before it's too late!
1. Chapter 1

A Mathematical Approach to Psych

A Psych/Numb3rs Crossover

By RascalFlattsS

Disclaimer: I don't own Psych or Numb3rs. The characters are properties of their owners. This is not written for publication purposes.

Author's Note: This is a crossover of both Psych and Numb3rs. I just thought it would be interesting to write a story between these two TV shows because they are both in the same local area and they also both solved crimes in two different ways. Plus, both Charlie and Shawn are not just hot, but have cops (or FBI agents) in the family. Plus Charlie already doesn't believe in psychics (see Season 2 of Numb3rs "Mind Games") so I always wondered how he would respond to Shawn. Enjoy.

Also, this takes place during season 4 of Numb3rs and season 2-3ish of Psych.

Chapter 1: Let's Bring Out the Consultants!

It was a beautiful sunny day in Santa Barbara, California. Except for another dead body found on the beach. Normally, even that wouldn't have put too much of a damper on the day, except that it was the sixth body found in the L.A. suburb area in the past three weeks. Which could only mean a serial killer was out running around the L.A. which no one really wants to think about.

Santa Barbara Police were called along with local FBI agents. Chief Karen Vick of the Santa Barbara Police Department, along with Head Detective Carlton Lassiter and his partner Detective Juliet O'Hara were already on the scene when the FBI SVU pulled up.

FBI agent Don Eppes stepped out of the driver's side. He glanced over towards the dead body. His attention turned when he heard the door of the passenger's side opened.

Everyone who saw Charlie Eppes knew he was Don's younger brother. And despite the fact that they were so similar, they were so different. Charlie had dark, curly brown hair where as his brother's was straight. Charlie was a mathematical genus working as a professor at CalSci. However Charlie did share his brother's passion for catching criminals and for the past three years had used his mathematical skills to helping his brother put criminals behind bars.

But no matter how much Charlie worked with Don, Charlie was still Don's little brother and Don tried to shield Charlie from the many horrors of his jobs. And looking at dead bodies that were tortured defiantly counted.

"Charlie," said Don stopping his younger brother. "Why don't you wait here by the car?"

Charlie shook his head, "Don, you don't need to protect me anymore. I've seen dead bodies before.

"But this is different," said Don. "This is…"

Charlie cut him off. "Don, I've already seen the photos of the victims. And I personally want to catch this guy and the more information I have, the better my equations are and the sooner we catch the SOB. So, let me do my job." And with that Charlie pushed Don's hand off his shoulder and walked towards the crime scene.

Don sighed as FBI agents, Colby Granger and David Sinclare walked up beside him. "What am I going to do with him?" Don asked.

"I don't know," said Colby, "Have him do all your math homework for you?"

Don pushed Colby and the three of them started walking towards the crime sense.

Charlie arrived at the tape and started to walk underneath when a hand grabbed him and turned him around, pining him against a pole, pinning his arms behind him. The clipboard, pencil and calculator fell to the ground.

"What are you doing?" asked Charlie.

"You are under arrest for trespassing at a crime scene and for obscuring justice," said SBPD head detective Carlton Lassiter, as he cuffed Charlie, "You have the right to remain silent…."

"WHAT THE HELL ARE YOU DOING?!" shouted Don. He, Colby and David ran up to Lassiter and Charlie. "Who the hell are you?"

"I am Head Detective Carlton Lassiter of the SBPD," said Lassiter, showing Don his badge, "I am arresting this man for trespassing on my crime scene. Who the hell are you?"

Don whipped out his badge, "FBI agent Don Eppes. And you have five seconds to let go of my brother or so help me God…"

Lassiter looked from Charlie to Don, "Your brother? You brought your brother to a crime scene?"

"Charlie is a consult for the FBI," said Colby. He and David were holding Don back from killing Lassiter. "He's a mathematician at CalSci."

"A mathematician?" repeated Lassiter. "Does he have clearance?"

"The highest," snarled Don. "Now. Let. Him. _Go_."

Lassiter sighed and pulled out a key and un-cuffed Charlie. Don reached forward and pulled Charlie away from Lassiter. "Are you alright?" asked Don.

"I'm fine," said Charlie. He picked up the clipboard and calculator and walked under the crime scene tape. Don gave Lassiter a death stare and then followed closely behind Charlie.

Lassiter sighed and ran his hand through his hair. And he though Shawn Spencer was a pain.

"Don't worry about it," said Colby. "Charlie is Don's little brother and about a month ago, Charlie became a target in an investigation. He was actually run off the road by these guys and they almost killed him. Don's been a little overprotected over Charlie since." Colby held out his hand to Lassiter. "I'm Colby Granger and this is David Sinclair."

Lassiter took his hand. "Carlton Lassiter." And with that the three of them walked towards the crime scene.

Don kept glaring at Lassiter but didn't say anything as the three of them walked up and listen to Chief Vick fill them in on the victim.

"And Professor Eppes, what exactly will you do?" asked Vick.

"I am a professor of applied mathematics at CalSci," said Charlie.

"He is also an FBI consultant," said Don, continuing to give Lassiter an evil glance.

"We'll we appreciate all the help we can get," said Vick. "However, we already have a consultant that we work with. And at the moment, he and his partner have a hundred percent closing rate."

"You already have another consultant?" asked Don. "Who?"

Just then, a blue Echo pulled up to the crime sense tape. Shawn Spencer and Burton "Gus" Guster stepped out of the car.

Shawn Spencer walked up to the crime sense tape, lifted it up and he and Gus walked underneath it.

"Lassie! Jules!" said Shawn. "What do I owe the pleasure?" Shawn turned and saw Charlie staring at him. "Who are you?"

"Mr. Spencer," said Vick. "Meet Professor Charlie Eppes from CalSci. He is a mathematical consultant for the FBI agent. Professor Eppes, meet Mr. Spencer. Mr. Spencer is our psychic consultant for the SBPD."

A/N: Hope you like it so far! Especially the part where Lassiter tries to arrest Charlie! Please R&R and let me know what you think!


	2. Chapter 2

Chapter 2: The Mathematical/Psychic Showdown

Charlie starred at Shawn in disbelief. "This guy," he said, point at Shawn. "Is a psychic?'

"Oh course, I'm a psychic," said Shawn.

"Oh really?" said Charlie. "I hardly believe that."

"You doubt me?" said Shawn. He put his hand over his heart. "That hurts my feelings."

"Okay," said Charlie. "Proof it. Prove you're a psychic."

Shawn brought his fingers and concentrated. He glanced at Charlie. Shawn noticed the calculations on the side of Charlie's clipboard, some of which were crossed out. He also noticed the picture of Charlie next to a pretty dark haired Indian woman with a date and time written with the name of a fancy restaurant. Shawn also noticed the similarities in facial features between Charlie and Don, assuming that they were probably related-most likely brothers. He also noticed a slight bruising around Charlie's wrists and how Don kept giving Lassiter evil glance out of the corner of his eye.

"You two," said Shawn, pointing to Don and Charlie, "are brothers. You, Professor Eppes are the younger brother. You've always looked up to your brother and have always wanted his approval.

"So?" said Charlie. "Everyone knows that Don and I are brothers. That's not exactly a secret."

"But wait, there's more," said Shawn. "Your two year anniversary is coming out with your girlfriend and you're ready to take a big step. Not marriage through." added Shawn, watching the look of horror coming across Charlie's face. "I'm sensing more along the lines of moving into together. I am also seeing that you are working on a major equation however you seem to have a case of writer's block. Or would that be math block? I'm not really sure."

Don turned to Charlie, "Is that true? Are you really stuck?"

Charlie turned bright red, "It's nothing. I just have to rework some of the equations. It's not a big deal."

"But wait, there's more… OUCH!" said Shawn grabbing his wrist. He then looked up at Don and Charlie and then turned to Don, "I wouldn't worry about Lassie trying to arrest Charlie-he tries to arrest me daily."

Everyone looked impressed-expect for Lassiter and Charlie.

"Wow," said Don. He held out his hand and Shawn took it. "Mr. Spencer, that was really good."

"Mr. Spencer is my father," said Shawn, "please call me Shawn."

"Shawn, it is," said Don. "I'm FBI Agent Don Eppes-and you've already meet Charlie-" Don pointed at his brother who did not smile back "-and this is FBI Agent Colby Granger-" Don pointed to the tall buff man with blonde hair and Shawn spotted the Marines tattoo on his arm "and this is FBI Agent David Sinclair." The tall black man nodded.

Shawn reached forward and shook Colby's hand. Colby was wearing a short sleeve shirt and Shawn noted part of a Marine tattoo on his arm. "It's a pleasure to meet you Agent Granger and I thank you for your service in Afghanistan with the Marines."

Colby looked shocked and then smiled. "Wow, Shawn that was very impressive."

"Thank you," said Shawn, making a little bow. He caught Charlie rolling his eyes and smiled. Shawn then turned to greet David.

"A pleasure to meet you Agent Sinclair," he said shaking David's hands. "This is my partner Gus, but you can just call him Big Headed Burton."

"Burton Guster," said Gus, shaking hands with David, Colby, Don and Charlie. He then turned to Shawn, "I told you not to call me that Shawn!"

"Why not?" asked Shawn. "It rolls off the tongue so well." He then turned back to the FBI agents, "And let me proudly introduced the finest detectives in the SBPD; the lovely Detective Juliet O'Hara-"Shawn pointed to the petite blonde detective-"the guy with a gruffly exterior but who has the heart of a giant teddy bear, Carlton Lassiter-"as Shawn pointed to Lassiter, he scowled- "and our wonderful and fabulous leader Chief Karen Vick."

"Thank you, Mr. Spencer," said Chief Vick. "Now that we all know each other, let's get back to the case."

"Right you are, Chief," said Shawn. He rubbed his hands together like a kid excited at Christmas. "So what do we have here?"

Charlie stiffened. "Someone was murdered here last night. Don't tell me that your psychic senses didn't tell you that?"

Shawn heard the sarcasm in his voice. "Oh course I knew that someone was murdered here last night, Professor. And I know that for two reasons: One, the sprits did tell me that and two, based on the fact that there is a dead body right here in front us is also a give away," Shawn said, his voice also full of sarcasm. "What I mean is _what_ do we know about our victim here. Lassie, you want to field this one?"

"Um, yes," said Lassiter. He glanced down at his notebook. "Unidentified male. Late 20's early 30's. Appears to have been shot in the back of the head. Suffered busing on torso, legs, arms and face. Wrist marks appear on both arms possible restrained. No personal items found."

"Nice wrap up, Lassie," said Shawn. He began to pace around the victim, studying him. "I will have to communicate with this poor man's sprit from beyond the grave to find out more information."

"Communicate with the dead? _Please,_" said Charlie. He turned to Don, "Listen Don, I can run a graph analysis on him and all the other victims and find out not only what they have in common but their links to the killer and why the killer is choosing them. Plus I can use another equation to figure out who the next victim will be," Charlie paused and turned backed to Shawn, glaring at him. "And I can do it _without_ looking into a crystal ball."

"I'm sure you can," said Shawn. "But I can find out everything we need to know simply by talking to the spirit of this young man and all the other victims. They can tell us all that, plus whom the killer is and where he'll strike next and I can do that without whipping out my graphing calculator."

"Shawn, you don't have a graphing calculator," said Gus.

"That's beside the point, Gus," said Shawn.

"Psychics aren't even real!" said Charlie.

"Oh really?" said Shawn. Charlie and Shawn were so close to each other that they were literally screaming in each other's faces. "Then how did I know everything about you?"

"Lucky guess!" said Charlie.

"Lucky guess?" repeated Shawn. "If that's the case, then I get lucky all the time then! What does your mathematical equation say about that?"

Colby turned to Don. "Don't you think that we should separate them or something?"

"Why?" asked Don. "It's not like they are going to start punching each other or something."

"I would say that it would be more like something," said David. Sure enough, Charlie and Shawn had started wrestling each other on the beach. At the moment, Shawn had Charlie in a head lock.

"Okay, break it up," said Don. Don and Colby jumped in and pulled the two men apart. Don held Charlie back while Colby held Shawn back.

"That's enough!" shouted Chief Vick. "There is a serial killer on the loose and you two are fighting like children! Well congratulations, boys. Because you two are now working together! I don't care how you solve this case wherever it's with math or psychic visions or black magic as long as you solve it! And if I hear about any more fighting, I will have Lassiter lock you up and throw away the key! Do I make myself clear?"

Charlie and Shawn looked at each other. It seemed they had no choice.

"Yes ma'am," they both replied.

"Excellent," said Chief Vick. "Now let's get to work."

Charlie walked towards Don. "Do I have to work with _that _guy?" he asked glancing over at Shawn.

Don shrugged his shoulders. "Yeah, it looks like it. Sorry, bro."

"But Don, you're the FBI!" said Charlie. "Surely you can get me out of it! Go over the Chief…"

"Only if I had a death wish," said Don. "I don't think I would stand a chance against Chief Vick." Don sighed. "Besides Charlie, it will do you some good to work with Shawn."

"But his methods are crazy!" said Charlie.

Don smiled, "Funny. I remember people saying the same thing when I brought you in as a consultant and that math could solve crimes. Look Charlie, I've heard about this guy, he's good. And we need the two of you working together so we can solve the case. The sooner we catch this guy the better."

Charlie nodded. Don walked over to talk with Colby and David, leaving Charlie to consider his new predicament

Shawn walked around the body, looking for clues for a psychic vision.

"Are you crazy, Shawn?" asked Gus.

"I would like to go with the obvious answer of 'yes', but that seems too easy," said Shawn.

"You had to pick a fight with Charlie Eppes!" said Gus, "Charlie Eppes! He is one of the best consultants the FBI has! Plus he's a brilliant mathematician! And an author! I read his book-it was pure genius! You had better be careful; or he'll come up an equation proving that you're not really psychic."

"Gus, don't be a cranky old lady," said Shawn. "First of all, I want to be partnered with Mr. Math because if I can convince him I'm a psychic then we will have a shot at getting into FBI cases as well as SBPD. Plus, he insulted my gift and now I'm going to prove that I'm just as good of a consultant as Mr. Math Professor."

Gus shrugged. There was no point in talking to Shawn anymore. He was stubborn and nothing Gus would say would change his mind.

Shawn continued to pace around the victim. The murderer had done a good job of making sure they couldn't id this victim by his face, thought Shawn.

Shawn suddenly stopped short. He paled. He spotted part of a tattoo on the victim's arm under his t-shirt. It was part of a Chinese letter for peace in blue ink. Shawn only knew of one person with a tattoo like that…

"Oh my God!" said Shawn. Everyone looked at him, shocked.

"What is it, Shawn?" asked Juliet. "Are you getting a vision?"

Shawn nodded, "I know who the victim is."

"Who?" asked Don.

"His name is Adam Harper," said Shawn.

"Harper," said Lassiter, tapping his pencil against his notebook. Then his eyes widened as the realization hit him. "As in Jake Harper?"

"I know I'm probably going to regret asking this," said Don. "But who's Jake Harper?"

"Jake Harper was my dad's old partner," said Shawn. "Adam is his son."

A/N: Let me know what you think!


End file.
